OXIDATION PROCESSES IN THE SOIL 525 



nitrification is entirely biological in nature, as established by Schloesing 

 and Miintz, 20 Warington 21 and others. 



Mechanism of ammonia oxidation. Various reactions have been 

 suggested to explain the mechanism of oxidation of ammonia to nitrite 

 by the nitrite forming bacteria. The following two reactions are most 

 probable : 



2 NH 3 4- 3 2 -> 2 HN0 2 + 2 H 2 (1) 



2 NH 3 + 30 2 -> N 2 3 + 3 H 2 (2) 



Godlewski 22 found that the ratio between the oxygen consumed in 

 the process and the nitrogen changed from the ammonia to the nitrite 



2 

 stage is 3, or R = — = 3. However, Schloesing 23 recorded previously 



JN2 



that this ratio varies from 4.57 to 5.57. The difference between these 

 results may be due to the fact that Schloesing made his determinations 

 in the soil as a medium while Godlewski carried out his studies in 

 solution. In the first instance, some of the oxygen was no doubt con- 

 sumed for other oxidation processes, in addition to nitrate formation. 

 Meyerhof 24 used the theoretical value of R = 3 for the calculation, 

 from the amount of oxygen consumed, of the quantity of nitrogen 

 oxidized from ammonia to nitrite. In a careful study of the gaseous 

 exchange in the reaction of oxidation of ammonia to nitrite, Bonazzi 25 

 demonstrated that the average value of R is 2.89 ± 0.08, which is very 

 close to 3.0, thus justifying the above equations. 



The presence of the carbonate is essential both as a source of 

 C0 2 (although the organism can also use free C0 2 present in the 

 atmosphere), and for keeping the medium properly buffered, pre- 

 venting it from becoming acid. Nitrites are formed also in an atmos- 



20 Schloesing, Th., and Miintz, A. Sur la nitrification par les ferments or- 

 ganises. Compt. Rend. Acad. Sci., 84: 301. 1877; 85: 1018. 1877; 86: 892. 

 1878; 89: 891, 1074. 1879. 



21 Warington, R. On nitrification. Jour. Chem. Soc, 33: 44-51. 1878; 

 35: 429-456. 



22 Godlewski, K. Uber die Nitrifikation des Ammoniaks und die Kohlen- 

 stoffquellen bei der Ernahrung der nitrifizierenden Fermente. Centrbl. Bakt. 

 II, 2: 458-462. 1896. 



23 Schloesing, Th. Sur la nitrification de l'ammoniaque. Compt. Rend., 109: 

 423-428, 883-887. 1885. 



24 Meyerhof, 1916 (p. 390). 



26 Bonazzi, A. On nitrification. V. The mechanism of ammonia oxidation. 

 Jour. Bact., 8: 343-363. 1923. 



